Alkylation process control method



Aug. 17, 1965 J. E. PHILLIPS ALKYLATION PROCESS CONTROL METHOD Filed March 29, 1962 INVENTOR. "1E` PHILLIPS A TTORNEJ/S United States Patent O 3,266,353 ALKYLATEN PRGCESS CNTRUL METHQD deck E. Phiilips, Eartiesviile, Ghia., assigner to Phiihps Petroieum Company, a corporation of Delaware Filed Mar. 29, 1962, Ser. No. 183,489 3 Claims. (Cl. 26d-683.d)

This invention relates to a method of and apparatus for controlling an alltylation process. In one specific aspect, this invention relates to a method of and apparatus for controlling the production of propane in an alkylation process.

The catalytic alkylation of an olefin with an isoparafin to form high-octane gasoline boiling range products is well known in the art. In a conventional alkylation process, an olefin feed comprising propylene and butylenes is passed with isobutane to an alkylation zone wherein the olefin and isobutane feed are contacted with liquid hydrofluoric acid, said hydrouoric acid acting as an alkylation catalyst. The alkylation zone hydrocarbon effluent is separated from the acid catalyst and fractionally separated with the isobutane and lighter hydrocarbon fraction recycled to the alkylation Zone.

The presence of inert materiais such as propane in the alkylation zone substantially decreases the efciency of the alkylation process. Therefore, it is desirable that the passage of inert materials such as propane to the alkylation zone be controlled and the production of inert materials such as Ipropane in the alkylation zone be minimized. It has been observed that the production of propane in the alkylation zone is directly proportional to the propane passed to the alkylation zone via the olen, fresh isobutane and recycled isobutane feed streams. With the recycle of the isobutane and lighter hydrocarbon fraction to the alkylation zone, the concentration of propane in the alkylation zone is continuously increased with the increased concentration subtracting from the eiiiciency of the alkylation process.

It has been discovered that the buildup of the propane concentration in the alkylation zone can be controlled by splitting the hydrocarbon effluent recovered from the alkylation zone and passing a portion of the hydrocarbon etiiuent through a first fractionation zone wherein rnaterials comprising propane and lower boiling materials are recovered overhead and removed from the alkylation process. The remainder of the alkylation Zone hydrocarbon effluent is combined with the depropanized bottoms from the first fractionation zone and passed to a second fractionation zone. Y

I have discovered a method of control and apparatus therefor whereby effective control of the concentration of propane in the alkylation Zone can be maintained. One embodiment of the inventive control system comprises determining the total rate of propane iiow to the allrylation Zone and manipulating the rate of hydrocarbon effluent flow to the first or depropanizing fractionation zone responsive thereto. A second embodiment of the inventive control system comprises determining the production of propane in the alkylation zone and manipulating the rate of alkylation Zone hydrocarbon eiiiuent iiow to the first or depropanizing fractionation zone responsive thereto.

Accordingly, an object of my invention is to provide an improved alkylation process.

Another object of my invention is to provide an improved method of and apparatus for controlling `the concentration of propane in an alkylation process.

Another object of my invention isto provide an improved method of and apparatus for controlling the separation of the hydrocarbon eiiiuent from an alkylation process.

3,2%,383 Faiaentecl Aug. 17, i965 lCe Other objects, advantages, and features of my invention will be readily apparent to those skilled in the art from the following description and the appended claims.

In the drawings:

FIGURE 1 is a schematic representation of one ernbodiment of the inventive control system.

FIGURE 2 is a schematic representation of another embodiment of the inventive control system.

The inventive method of control and apparatus therefor is applicable to an allrylation process wherein an oleiin is contactedwith an isoparaiidn in the presence of an alkylating catalyst such as hydroiiuoric acid, sulfuric acid, phosphoric acid, or a metal halide with a hydrogen halide promoter. The olefin is selected from the group of oleiins having 3-5 carbon atoms per molecule or mixtures thereof and the isoparaffin is selected from the group consisting of isobutane and isopentane.

Referring to FIGURE 1, an olefin feed is passed via conduit means 11 to alkylation zone 16. Fresh alkylating agent comprising an isoparaiiin is passed via conduit means 16 to alkylation Zone 10. A recycle isoparafiin stream from a source hereinafter described is combined with the isoparaiiin stream in conduit 1e and passed to allrylation zone 10. Catalyst is introduced to alkylation zone 1t) via conduit means 24. Recycle catalyst is withdrawn from phase separation zone 21 and passed to alkylation Zone 1t) via conduit means 22, conduit means 23 and conduit means 24.

Conventional alkylation conditions are maintained within alkylation zone lil. For example, assuming that the olefin feed comprises propylene and butylenes, the alkylating agent comprises `isobutane and the catalyst comprises hydroiiuoric acid, the temperature of the alkylation zone 10 is preferably maintained in the range of between about EES- F. with the pressure of alkylation Zone 10 sufficient to maintain a liquid phase reaction. The volume ratio of acid to hydrocarbon maintained in the alkylation zone 10 is preferably in the range from about821to 0.8:1. p

The inventive control system will hereinafter be described as applied to an alkylation process wherein an olefin feed comprising propylene and butylenes is contacted with isobutane in the presence of an acid catalyst.

It is not, however, intended that the inventive` control system should be limited thereto.

The alkylation zone effluent mixture is passed via conduit means 20 to a phase separation zone 2-1 wherein the acid catalyst is separated from the hydrocarbon phase. As previously noted, the acid phase is withdrawn from phase separation zone 21 via conduit means 22 and recycled via conduit means 23 and conduit means 24 to alkylation Zone 10. A hydrocarbon phase is withdrawn from phase separation zone 21 via conduit means 26. A portion of the hydrocarbon phase withdrawn from phase separation Zone 21 via conduit means 26 is passed via control valve means 28 and conduit means 25 to fractionation or depropanizing zone 30. The remainder of the hydrocarbon phase withdrawn from phase separation zone 21 is passed via conduit means 26 and conduit means 27 to a deisobutanizing or second fractionation zone 33.

Within depropanizing zone Sti, a hydrocarbon feed stream is fractionated into a propane and llighter fraction withdrawn from depropanizing zone 3@ via conduit means 31 and a hydrocarbon fraction withdrawn from depropanizing Zone 30 via conduit means 32. Depropanizing zone 30 can conventionally comprise a depropanizing coiurnn with a means of condensing a vaporous overhead stream withdrawn from the depropanizer column, a means of withdrawing a bottom product stream and a means for recycling a portion of the condensed vapor stream to the depropanizer column as reflux. The depropanizing col- Y isobutanizing column, a means of withdrawing a vaporous overhead stream, condensing said vaporous overhead stream and recycling at least a portion of the condensed vaporous stream to the deisobutaniznig column as reilux, and a means of withdrawing a bottom product stream from the deisobutanizing column. The bottom temperature and pressure of the deisobutanizing column is generally maintained in the range of Z50-290 F. land in the range of D-125 p.s.i.g., respectively. A liquid isobutane containing stream is Withdrawn from deisobutanizing zone 33 via conduit means 36 and recycled to lalkylation zone 10 via conduit means 16. A hydrocarbon stream comprising n-butane and alkylate is withdrawn from deisobutanizing zone 33 via conduit means 34 and passed to a conventional hydrocarbon separation process such as a fractionation zone, such as a debutanizer, wherein alkylate is separated from the hydrocarbon stream Withdrawn from deisobutanizing zone 33.

Having described the process flowing, reference is made to FIGURE l for a description of one embodiment of the inventive control system. The olen feed flowing conduit 11 is analyzed by a conventional analyzer 12 such as a chromatographic analyzer, which includes a recordertransmitter. Instrumentation of this type is manufactured by Perkin-Elmer Corporation and others. When employing a chromatographic analyzer-recorder-transmitter, a peak reading and holding device such as described in' ISA Journal 9, page 28, October 1958, will transmit the analog of the concentration of the component of interest, in this case propane, in conduit 11 to an analog computer 14. In the same manner, an analyzer-recorder-transmitter 17 can be utilized to analyze the feed stream flowing through conduit 16 and the analog of the concentration of propane transmitted to computer 19. An analyzer-recorder-transmitter 38 can be utilized to analyze the recycle stream owing through conduit 36 and the analog of the concentration of propane transmitted to computer 39. It is within the scope this invention to eliminate analyzerrecorder-transmitters 17 and 38 and computers 19 and 39 and to employ a single analyzer-recorder-transmitter and a single computer to analyze the combined isoparain feed stream in conduit 16 and to receive the analog of the concentration of propane in said combined isoparaffin feed stream' When employing a chromatographic analyzer to analyze the alkylation zone feed streams, the output of the peak reader is an electrical signal in the range of 0-50 volts D C. Computers 14, 19 and 39 can, therefore, be conventional small analog computers capable of multiplying one input signal by another input signal to produce an output signal representative of the product of said signals. An analog computer capable of performing this operation is Model TR-lO manufactured by Electronic Associates, Long Branch, New Jersey.

The rate of iuid flow through conduit means 11 is sensed by a conventional rate of fiow sensing means and a signal representative of said rate of flow transmitted by an transmitter 13 to computer 14. In like manner, rates of iiuid flow through conduit means 16 and conduit means 36 are sensed and signals representative of said rates of flow are transmitted via transmitters 18 and 3,7

'to computers 19 and 39, respectively.

Computers 14, v19 and 39 multiply the heretofore described signals in the prescribed manner and transmit signals representative of the rate of propane flow in conduits 11, 16 and 36, respectively, to a computer 44B. Transmitters 13, 18 and 37 transmit signals representative of fluid iiows through conduit means 11, 16 and 36, respectively, to a conventional relay 41, said relay 41 capable of summing the three input signals and transmitting a signal representative of the total to computer 40. A relay capable of performing this operation is the Moore M/F Computing Relay, Moore Products Co., Philadelphia, Pa., with E.M.F.topneumatic transducers capable of transforming input signals to pneumatic pressures and of transforming `an output pneumatic pressure signal to an signal.

Computer 40 is an instrument capable of summing the input signals received from computers 14, 19 and 39 and dividing the total by a signal received from relay 41 to produce a signal representative of the rate of propane' How per unit of total hydrocarbon feed ow to alkylation zone 1t). As in the case of computer 14, computer 4t) can be a conventional small analog computer Model TR-l() manufactured by Electronic Associates, Long Branch, New Jersey. Computer 40 transmits a signal representative of the rate of propane low per unit of total hydrocarbon feed tlow to a conventional propane-recordercontroller 35, having a set point representative of the desired rate of propane ow to alkylation zone 10 per unit volume of total hydrocarbon feed ow.

Propane-recorder-controller 35 transmits a signal to a conventional How-recorder-controller 29 as a reset signal. Flow-recorder-controller 29 opens or closes valve 28 responsive to said reset signal and to a rate of ow measurement in conduit 25, thereby manipulating the rate of fluid flow to depropanizing zone 30 so as to maintain the rate of propane ow per unit volume of total hydrocarbon feed flow to alkylation zone 10 constant.

Referring to FIGURE 2, therein is illustrated a second embodiment of the inventive control system. As in the case of FIGURE 1, computer 14 transmits a signal representative of the rate of propane flow through conduit means 11, said signal transmitted to a conventional adding relay 50. In FIGURE 2, computer 19 transmits a signal representative of the rate of propane ow in the combined isoparan feed stream to adding relay 50.

A hydrocarbon alkylation zone eluent stream flowing through conduit 26 is analyzed by a conventional analyzer 52 such as the previously described chromatographic analyzer. A signal representative of the concentration of propane inthe hydrocarbon effluent is transmitted from .analyzer-recorder-transmitter 52 to a computer 51. A signal representative of the rate 'of iluid flow through conduit means 26 is transmitted by transmitter 53 to computer 51. Like computer 14, computer 51 can be a Model TR-lO manufactured by Electronic Associates capable of transmitting a signal representative of the rate of propane ilow through conduit means 26 to adding relay 50.

Adding relay 50 is a conventional instrument such as Moore M/I;` Computing Relay, Moore Products, Philadelphia, Pa., with E.M.F.to-pneumatic transducers capable of transforming input signals to pneumatic pressures and of transforming an output pneumatic pressure signal to an signal, and capable of solving the following equation:

OutputzC- (A -l-B) where A is equal to the signal received from computer 14; B is equal to the signal received from computer 19; and C is the signal received from computer 51. Adding relay S0 transmits a signal representative of the propane produced in alkylation zone 10 per unit volume of total hydrocarbon feed flow to a propane-recorder-controller 54 having a set point representative of the desired propaneproduction. Propane-recorder-controller 54 transmits a reset signal to how-recorder-controller 29. Flow-recordertration within alkylation zone in the range of about 5-6 volume percent of the hydrocarbon phase so as to suppress the formation of propane at the expense of alkylate within alkylation zone 1f). With respect to FIG- URE 2., preferably the set point of propane-recordcr-controller 54 is representative of zero.

Referring to FIGURE 1, let it be assumed that the rate of flow of propane to yalkylation zone 10 via the olefin feed is l() barrels per stream day (b.p.s.d.). Let it further be assumed that the rate of flow of propane to alkylation zone 1) via the fresh isobutane feed is 3 b.p.s.d., the rate of ow of propane to alkylation zone 10 via the recycle isobutane stream is 70 yb.p.s.d., and the total hydrocarbon rate of flow to alkylation zone 10 is 1,000 b.p.s.d. A signal re-presentative of the iiow rate of l0 b.p.s.d. will be transmitted from computer 14 to computer 4). A signal representative of a ow rate of 3 b.p.s.d. will be transmitted from computer 19 to computer 40. A signal representative of a rate of ow of 70 b.p.s.d. will be transmitted from computer 39 to computer 40. A signal representative of 1,000V b.p.s.d. will be transmitted from adding relay 41 to computer 40. A signal wiil be transmitted from computer 40 to propane-recorder-controller 35 representative `of a` propane concentration of .083 barrel of propane per barrel of hydrocarbon feed to alkylation zone 10. This signal received from computer 4) is compared with a set point signal representative of .050 barrel of propane per barrel of tot-al hydrocarbon feed to alkylation zone 1i). Propane-recorder-controller 35 will transmit a reset signal to fiow-recorder-controller 29. Flowrecordercontroller 29 will cause control valve 28 to open, thereby increasing the rate of ow of alkylation zone hydrocarbon etiiuent to depropaniz-ing zone Si?. By increasing the rate of fiow of alkylation zone hydrocarbon effluent to depropan-izing zone 30, the concentration of propane in the recycle isobutane stream is reduced, thereby reducing the concentration of propane in alkylation zone 10 to a desired 5 Volume percent.

If the signal transmitted from computer 4f) to propanerecorder-controller 35 would represent a propane concentration less than .05 barrel per barrel of total hydrocarbon feed to alkylation zone 10, then the reset signal transmitted to fiow-recorder-controller 29 would result in the closing of valve 28. By decreasing the flow of alkylation zone hydrocarbon effluent to depropanizing zone 3d, the rate of flow of propane with the recycle isobutane stream in conduit 36 is increased, thereby increasing the concentration of propane in alkylation zone 1) to the desired level.

It is Within the scope of this invention to employ conventional pneumatic control instruments and computers in the manner prescribed for the electronic instruments herein illustrated.

As will be evident to those skilled in the art, Various modifications of this invention can be made, or followed, in the light of the foregoing disclosure and discussion without departing from the spirit or the scope thereof.

I claim:

1. In an alkylation process which comprises passing a stream containing an olefin having 3-5 carbon atoms per molecule to an alkylation zone containing an alkylation catalyst, passing a stream containing an isoparaffin selected from the group consisting of isobutane and isopentane to said alkylation zone, separating an alkylation zone hydrocarbon efiiuent from said alkylating catalyst, passing at least a portion of said alkylation zone hydrocarbon effluent to a fractionation zone, withdrawing an alkylate fraction from said fractionation zone, and passing a fraction containing an isoparafiin from said fractionation zone to said alkylation zone; a method of control which comprises measuring at least one property of said olefin stream passed to said alkylation zone representative of the rate of flow of propane contained therein, measuring at least one property of the isoparafn feed to said alkylation zone representative of the rate of flow of propane contained therein, and manipulating the rate of flow of said alkylation zone hydrocarbon effluent to a depropanizing zone respons-ive to the total rate of flow of propane to said alkylation zone.

2. The ymethod of control of claim 1 whe-rein said olen stream comprises a mixture of propylene and butylenes and said isoparafiin comprises isobutane.

3. ln an alkylation process which comprises passing a stream containing an olefin having 3-5 carbon atoms per molecule to an alkylation zone containing an alkylation catalyst, passing a stream containing an isoparaffin selected from the group consisting of isobutane and isopentane to said alkylation zone, separating an alkylation zone hydrocarbon effluent from said alkylating catalyst, passing at least a portion of said alkylation zone hydrocarbon effluent to a fractionation zone, withdrawing 4an alkyiate fraction from said fractionation zone, and .passing a fraction containing an isoparafiin from said fractionation zone to said alkylation zone; a method of control which comprises measuring at least one property of said olefin stream representative of the rate of flow of propane contained therein, measuring at least one property of the isoparafiin passed to said alkylation zone representative of the rate of flow of propane contained therein, measuring at least one property of the alkylation zone hydrocarbon efiiuent representative of the rate of iiow of propane contained therein, and manipulating the rate of ow of said alkylation zone hydrocarbon efliuent to a depropanizing zone responsive to the propane produced in said alkylation zone.

4. The method of control of claim 3 wherein said olefin stream comprises a mixture of propylene `and butylenes and said isoparaiiin comprises isobutane.

5. In an alkylation process which comprises passing a stream containing an olefin having 3-5 carbon atoms per molecule to an alkylation zone containing an alkylation catalyst, passing a stream containing an isoparafiin selected from the group consisting of isobutane and isopentane to said alkylation zone, separating the alkylation zone hydrocarbon efliuent from said alkylating catalyst, passing at least a portion of said alkylation zone hydrocarbon effluent to a fractionation zone, withdrawing an alkylate fraction from said fractionation zone, and passing a fraction containing an isoparafiin from said fractionation zone to said alkylation zone; a method of control Which comprises measuring a property of said olefin stream representative of the concentration of propane contained therein and passing a first signal representative of said measurement to a first computing zone, passing a second signal representative of the rate of flow of said olefin to said first computing zone, measuring a property of the isoparafiin feed to said alkylation zone representative of the concentration of propane contained therein and passing a third signal representative of said measurement to a second computing zone, passing a fourth signal t0 said second computing zone representative of the isoparaiiin rate of flow to said alkylation zone, passing a fifth signal from said first computing zone to a third computing zone representative of the rate of flow of propane in said olefin passed to said alkylation zone, passing a sixth signal from said second computing zone to said third computing zone representative of the rate of flow of propane in said isoparaffin passed to said alkylation zone, and passing a seventh signal representative of the total rate of flow of propane to said alkylation zone from said third computing zone to a means for manipulating the rate of alkylation zone hydrocarbon effluent fiow to a depropanizing zone.

6. In an alkylation process which comprises passing a stream containing an olefin having 3-5 carbon atoms per Vmolecule to an alkylation zone containing an alkylation catalyst, passing a stream containing an isoparain selected from the group consisting of isobutane and isopentane to said alkylation zone, separating the alkylation zone hydrocarbon effluent from said alkylating catalyst, passing at least a portion of said alkylation zone hydrocarbon effluent to a fractionation zone, withdrawing an alkylate fraction from said fractionation zone and passing a fraction containing an isoparan from said fractionation zone to said alkylation zone; the method of control which comprises measuring a property of said olefin stream representative of the concentration ofpropane contained therein and passing a first signal representative of said measurement to a first computing zone, passing a second signal representative of the rate of ow of said olefin to said rst computing zone, measuring a property of the isoparaiiin feed to said alkylation zone representative of the concentration of propane contained therein and passing a third signal representative of said measurement t-o a second computing zone, passing a fourth signal to said computing zone `representative of the iso- 4paraffin rate of flow to said alkylation zone, measuring a property of said alkylation zone hydrocarbon effluent representative of the concentration of propane contained `therein and passing a fifth signal representative of said measurement to a third computing zone, passing a sixth signal to said thi-rd computing zone representative of the rate of ow of said alkylation zone hydrocarbon eftluent from said alkylation zone, passing a seventh signal from said first computing zone to a fourth computing zone representative of the rate of flow of propane in said olefin passed to said alkylation zone, passing an eighth signal from said second computing zone to said fourth computing zone representative of the rate of flow of propane in said isoparafn passed to said alkylation zone, passing a ninth signal from said third computing zone to said fourth computing zone representative of the rate of flow of propane in said alkylation zone efuent withdrawn from said alkylation zone, and passing a tenth signal representative of the propane produced in said alkylation zone from said fourth computing zone to a means for manipulating the rate of alkylation zone hydrocarbon eifiuent ow to a depropanizing zone.

7. The method of cont-rol of claim 5 wherein said olefin stream comprises a mixture of propylene and butylenes and said isoparafin comprises isobutane.

8. The method of control of claim 6 wherein said olefin stream comprises a mixture of propylene and butylenes and said isoparan comprises isobutane.

References Cited by the Examiner UNITED STATES PATENTS 2,764,623 9/56 Leonard et al. 26o-683.48 2,910,521 10/59 Cobb 26o-683.48 2,929,857 3/60 Hutto 260-683.48 2,990,437 6/61 Berger 260--683-48 X 3,018,230 1/62 Morgan 202-160 3,018,310 1/62 Van Pool 260-683.48 3,085,050 4/63 Kleiss 202-160 ALPHONSO D. SULLIVAN, Primary Examiner.

VDANIEL E. WYMAN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,200,883 August l7, 1965 Jack E. Phillips It is hereby Certified that error appears n the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, line 22, after "said" insert second Signed and sealed this 22nd day of March 1966.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD I. BRENNER Commissioner of Patents 

1. IN AN ALKYLATION PROCESS WHICH COMPRISES PASSING A STREAM CONTAINING AN OLEFIN HAVING 3-5 CARBON ATOMS PER MOLECULE TO AN ALKYLATION ZONE CONTAINING AN ALKYLATION CATALYST, PASSING A STREAM CONTAINING AN ISOPAARAFFIN SELECTED FROM THE GROUP CONSISTING OF ISOBUTANE AND ISOPENTANE TO SAID ALKYLATIN ZONE, SEPARATING AN ALKYLATION ZONE HYDROCARBON EFFLUENT FROM SAID ALKYLATING CATALYST, PASSING AT LEAST A PORTION OF SAID ALKYLATING CATALYST, CARBON EFFLUENT TO A FRACTIONATION ZONE, WITHDRAWING AN ALKYLATE FRACTION FROM SAID FRACTIONATION ZONE, AND PASSING A FRACTION CONTAINING AN ISOPARAFFIN FROM SAID FRACTTIONATION ZONE TO SAID ALKYLATION ZONE; A METHOD OF CONTROL WHICH COMPRISES MEASURING AT LEAST ONE PORPERTY OF SAID OLEFIN STREAMF PASSED TO SAID ALKYLATIN ZONE REPRESENTATIVE OF THE RATE OF FLOW OF PROPANE CONTAINED THEREIN, MEASURING AT LEAST ONE PROPERTY OF THE SSOPARAFFIN FEED TO SAID ALKYLATIN ZONE REPRESENTATIVE OF THE RATE OF FLOW OF PROPANE CONTAINED THEREIN, AND MANIPULATING THE RATE OF FLOW SAID ALKYLATIN ZONE HYDROCARBON EFFLUENT TO A DEPROPANIZING ZONE RESPONSIVE TO THE TOTAL RATE OF FLOW OF PROPANE TO SAID ALKYLATION ZONE. 